Difficulties in maintaining long-term partial nitritation of ammonium-rich sludge digester liquids in a moving-bed biofilm reactor (MBBR)

Abstract

Nitrogen can be eliminated effectively from sludge digester effluents by anaerobic ammonium oxidation (anammox), but 55-60% of the ammonium must first be oxidized to nitrite. Although a continuous flow stirred tank reactor (CSTR) with suspended biomass could be used, its hydraulic dilution rate is limited to 0.8-1 d(-1) (30 degrees C). Higher specific nitrite production rates can be achieved by sludge retention, as shown here for a moving-bed biofilm reactor (MBBR) with Kaldnes carriers on laboratory and pilot scales. The maximum nitrite production rate amounted to 2.7 gNO2-Nm(-2)d(-1) (3 gO2m(-3)d(-1), 30.5 degrees C), thus doubling the dilution rate compared to CSTR operation with suspended biomass for a supernatant with 700 gNH4-Nm(-3). Whenever the available alkalinity was fully consumed, an optimal amount of nitrite was produced. However, a significant amount of nitrate was produced after 11 months of operation, making the effluent unsuitable for anaerobic ammonium oxidation. Because the sludge retention time (SRT) is relatively long in biofilm systems, slow growth of nitrite oxidizers occurs. None of the selection criteria applied - a high ammonium loading rate, high free ammonia or low oxygen concentration - led to selective suppression of nitrite oxidation. A CSTR or SBR with suspended biomass is consequently recommended for full-scale operation.

Nitrous oxide emissions in a biofilm loaded with different mixtures of concentrated household wastewater

“…With a reactor pH of 8.0-8.5, the oxidation of NO 2 -was most likely inhibited by free NH 3 as reported by earlier studies (e.g. Fux et al 2004). Applying a classical inhibition model (Anthonisen et al 1976) to our reactor tanks resulted in a 20-30 % inhibition of NO 2 -oxidation for P1, 50-60 % for P2 and 60-70 % for P3, supporting the assumption that NH 3 inhibited nitrite oxidation.…”

“…MBBR systems are simple to operate and monitor at steady state and therefore often used in applied biofilm experiments (e.g. de Graaff et al 2010;Fux et al 2004). Moreover, simple MBBR systems are typically used in decentralized applications, in which nitrification is not necessarily the main purpose but often occurs as a side effect (Daude and Stephenson 2003).…”

The Effect of Influent Characteristics and Operational Conditions over the Performance and Microbial Community Structure of Partial Nitritation Reactors

“…It has been stated that AOB become inhibited by FA and FNA when nitrogen loading rates become higher than 1.5 kg/m −3 day −1 [43]. Regardless of this, the adaptation of NOB and AOB communities to FA concentrations has been widely covered by several authors [44][45][46] [24]. Therefore, control based on FA concentrations might not be an efficient, practical tool for the assessment of the performance of partial nitritation systems.…”

Development of the First Russian Anammox-Based Technology for Nitrogen Removal from Wastewater

“…The filtrate from dewatering centrifuges was passed through the grid (1) for removal of coarse particles and was then collected in the receiving tank (2). From this tank the filtrate was transferred to the 4-m 3 primary settler (3), then to the heat exchanger (4), and subsequently to the 20-m 3 main bioreactor (5). The setup was designed for carrying out the intended processes of water treatment within a broad range of operating temperatures (from 20 to 37°C).…”